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P H Y S I C S Chapter 5: Momentum Section 5C : Conservation of Momentum (Elastic Collisions)

P H Y S I C S Chapter 5: Momentum Section 5C : Conservation of Momentum (Elastic Collisions). Bell Ringer. A 40 kg miniature horse runs west at 8m/s. What is the force of impact if it hits a wall and comes to a stop in .5s?. Elastic Collisions. O bjects move separately after collision

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P H Y S I C S Chapter 5: Momentum Section 5C : Conservation of Momentum (Elastic Collisions)

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  1. P H Y S I C S Chapter 5: Momentum Section 5C: Conservation of Momentum (Elastic Collisions)

  2. Bell Ringer • A 40 kg miniature horse runs west at 8m/s. What is the force of impact if it hits a wall and comes to a stop in .5s?

  3. Elastic Collisions • Objects move separately after collision • KE is conserved • p is conserved

  4. Conservation of Momentum • Principle that states that the total momentum of an isolated system stays constant. • Total momentum before a collision equals total momentum after a collision p = 20 kg·m/s p = 30 kg·m/s p = 20 kg·m/s p = 30 kg·m/s Total = 50 kg·m/s Total = 50 kg·m/s

  5. Conservation of Momentum Equation Unit: • po (total)  sum of initial momenta of all objects • p(total)  sum of final momenta of all objects * Remember that velocities are vectors

  6. Conservation of Momentumin Space

  7. Demo: Newton’s Cradle

  8. Newton’s Cradle

  9. Demo: Basketball and Tennis Ball

  10. Conservation of Momentumin Two Dimensions

  11. Conservation of Momentumin Two Dimensions After Before

  12. In-Class Problem #1 After a hold up, Robin Banks flees in his 1575 kg getaway car at 20 m/s. He crashes into a 45 kg highway barrel which is at rest. If Robin Bank’s car moves at 18.9 m/s after the collision, how fast does the barrel move after being hit? v = 38.9 m/s

  13. Types of Collisions • Elastic • Inelastic • Perfectly inelastic

  14. Types of Collisions

  15. Conservation of Momentum • Principle that states the total momentum of an isolated system stays constant p = 20 kg·m/s p = 40 kg·m/s Total = 60 kg·m/s Total = 60 kg·m/s

  16. Examples ofPerfectly Inelastic Collisions

  17. Conservation of Momentum Equation Unit: • po (total)  sum of initial momenta of all objects • p(total)  sum of final momenta of all objects * Remember that velocities are vectors

  18. In-Class Problem #1 A 1950 kg police car going 12.5 m/s rear-ends a 1500 kg sedan moving at 3.0 m/s. After the collision the two cars move together as one unit. What is their final velocity? v = 8.37 m/s

  19. In-Class Problem #2 A 79.5 kg defensive endtackles a 60 kg running back going north at 5 m/s. After the hit both players move together at 2.5 m/s south. How fast was the defensive end running before the tackle? v = 8.16 m/s south

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